Fix belt purge tower activation and placement safety

result.json

@@ -1,10 +0,0 @@
-{
-	"error_string": "Success.",
-	"export_time": 0,
-	"layer_height": 0.0,
-	"plate_index": 0,
-	"prepare_time": 0,
-	"return_code": 0,
-	"sparse_infill_density": 0.0,
-	"wall_loops": 0
-}

src/libslic3r/BeltPurge.cpp

@@ -42,10 +42,15 @@ bool Print::has_belt_purge_tower() const
 {
     // Its own purge-tower "type", gated by the belt-only enable_belt_purge_tower
     // option (not the classic enable_prime_tower).
-    return m_config.belt_printer.value
-        && m_config.enable_belt_purge_tower.value
-        && !m_config.spiral_mode.value
-        && m_config.filament_diameter.values.size() > 1;
+    if (!(m_config.belt_printer.value
+          && m_config.enable_belt_purge_tower.value
+          && !m_config.spiral_mode.value
+          && m_config.filament_diameter.values.size() > 1))
+        return false;
+
+    return std::any_of(m_objects.begin(), m_objects.end(), [](const PrintObject *object) {
+        return object->config().belt_purge_tower_object.value;
+    });
 }
 
 // Belt mode: align ALL objects on the plate (the printed objects AND the purge

src/libslic3r/GCode/ToolOrdering.hpp

@@ -50,7 +50,7 @@ public:
     // tower to tell which prism fills carry purge vs. which are unclaimed waste.
     bool is_entity_overridden(const ExtrusionEntity* entity, const PrintObject *object, size_t copy_id) const {
         auto it = entity_map.find(std::make_tuple(entity, object));
-        return it == entity_map.end() ? false : it->second[copy_id] != -1;
+        return it != entity_map.end() && copy_id < it->second.size() && it->second[copy_id] != -1;
     }
 
     bool is_overriddable(const ExtrusionEntityCollection& ee, const PrintConfig& print_config, const PrintObject& object, const PrintRegion& region) const;

src/libslic3r/Print.cpp

@@ -1477,13 +1477,13 @@ StringObjectException Print::validate(std::vector<StringObjectException> *warnin
 
     if (m_config.belt_printer.value && m_config.enable_belt_purge_tower.value
         && m_config.print_sequence == PrintSequence::ByObject
-        && extruders.size() > 1 && warning != nullptr) {
+        && extruders.size() > 1) {
         StringObjectException warningtemp;
         warningtemp.string     = L("The belt purge tower is not generated in \"By object\" print sequence; "
                                    "filament changes will not be purged.");
         warningtemp.opt_key    = "enable_belt_purge_tower";
         warningtemp.is_warning = true;
-        *warning               = warningtemp;
+        add_warning(warningtemp);
     }
 
     if (m_config.enable_prime_tower) {

src/slic3r/GUI/BeltPurgeTower.cpp

@@ -142,7 +142,14 @@ bool ensure_belt_purge_tower(Model &model, PartPlateList &partplate_list, Object
     }
 
     // --- Sizing -----------------------------------------------------------
-    const double width   = print_config.has("belt_purge_tower_width") ? std::max(1., print_config.opt_float("belt_purge_tower_width")) : 35.;
+    const int    n_islands = std::max(1, (int) filaments.size() - 1);
+    const double gap       = 1.0;
+    // Every disconnected island needs at least 1 mm of printable width. Honor
+    // the configured total width whenever possible, but never let the island
+    // layout silently grow past the footprint used for placement.
+    const double min_width = n_islands + (n_islands - 1) * gap;
+    const double width     = std::max(min_width,
+        print_config.has("belt_purge_tower_width") ? print_config.opt_float("belt_purge_tower_width") : 35.);
     const double layer_h = print_config.has("layer_height") ? print_config.opt_float("layer_height") : 0.2;
 
     // Belt geometry. The rotation axis is the gantry tilt axis; the belt
@@ -219,6 +226,9 @@ bool ensure_belt_purge_tower(Model &model, PartPlateList &partplate_list, Object
     new_sig.key[4] = q(belt_max);
     new_sig.key[5] = q(lat_min);
     new_sig.key[6] = q(z_max);
+    new_sig.key[7] = static_cast<long>(rot);
+    new_sig.key[8] = std::lround(theta * 10000.0);
+    new_sig.key[9] = q(lat_max);
     if (prism_idxs.size() == 1 && new_sig == sig)
         return false; // already up to date — do not touch the model
 
@@ -279,15 +289,13 @@ bool ensure_belt_purge_tower(Model &model, PartPlateList &partplate_list, Object
     // lets each swap claim its own island. Total lateral footprint stays `width`
     // (each island width/N wide, separated by a small gap), so per-layer capacity
     // per island ~= max_flush, matching the height sizing.
-    const int    n_islands = std::max(1, (int) filaments.size() - 1);
     // Minimal gap between sub-bars: they must stay just-separated so the slicer
     // keeps them as distinct islands (hence distinct infill collections, one per
     // simultaneous swap). Zero gap would union them into one collection and
     // reintroduce the multi-swap-per-layer absorption bug; a hair over ~2 line
     // widths also keeps gap-fill from bridging them. 1 mm is about as close as
     // they can butt up while staying individually purgeable.
-    const double gap       = 1.0;
-    const double w_sub     = std::max(1.0, (width - (n_islands - 1) * gap) / n_islands);
+    const double w_sub = (width - (n_islands - 1) * gap) / n_islands;
 
     // --- (Re)create ---------------------------------------------------------
     if (!prism_idxs.empty())

src/slic3r/GUI/BeltPurgeTower.hpp

@@ -1,5 +1,4 @@
-#ifndef slic3r_GUI_BeltPurgeTower_hpp_
-#define slic3r_GUI_BeltPurgeTower_hpp_
+#pragma once
 
 // ORCA-Belt: auto-managed purge prism for belt printers.
 //
@@ -23,12 +22,12 @@ struct BeltPurgeSignature
 {
     bool valid          = false;
     int  filament_count = 0;
-    long key[7]         = {0}; // rounded geometry inputs (0.1 mm units)
+    long key[10]        = {0}; // rounded geometry inputs (0.1 mm units)
     bool operator==(const BeltPurgeSignature &o) const
     {
         if (valid != o.valid || filament_count != o.filament_count)
             return false;
-        for (int i = 0; i < 7; ++i)
+        for (int i = 0; i < 10; ++i)
             if (key[i] != o.key[i])
                 return false;
         return true;
@@ -44,5 +43,3 @@ bool ensure_belt_purge_tower(Model &model, PartPlateList &partplate_list, Object
 
 } // namespace GUI
 } // namespace Slic3r
-
-#endif // slic3r_GUI_BeltPurgeTower_hpp_

tests/fff_print/test_print.cpp

@@ -300,6 +300,41 @@ TEST_CASE("Print::validate tolerates a null warnings pointer", "[Print][validate
     CHECK(err.string.empty());
 }
 
+TEST_CASE("Purge tower selection keeps ordinary printers on the classic path", "[Print][PurgeTower][Regression]")
+{
+    DynamicPrintConfig config = multifilament_config(2, {
+        { "belt_printer",            0 },
+        { "enable_prime_tower",      1 },
+        { "enable_belt_purge_tower", 1 }
+    });
+    config.set_key_value("timelapse_type", new ConfigOptionEnum<TimelapseType>(TimelapseType::tlSmooth));
+
+    Model model;
+    Print print;
+    build_cubes(model, print, config, /*n=*/1, /*overlap=*/false);
+
+    CHECK(print.has_wipe_tower());
+    CHECK_FALSE(print.has_belt_purge_tower());
+}
+
+TEST_CASE("Belt purge planning requires its managed purge object", "[Print][PurgeTower][Regression]")
+{
+    DynamicPrintConfig config = multifilament_config(2, {
+        { "belt_printer",             1 },
+        { "enable_belt_purge_tower", 1 }
+    });
+
+    Model model;
+    Print print;
+    build_cubes(model, print, config, /*n=*/1, /*overlap=*/false);
+    CHECK_FALSE(print.has_belt_purge_tower());
+
+    model.objects.front()->config.set_key_value("belt_purge_tower_object", new ConfigOptionBool(true));
+    print.apply(model, config);
+    CHECK(print.has_belt_purge_tower());
+    CHECK_FALSE(print.has_wipe_tower());
+}
+
 TEST_CASE("A default slice emits perimeter, infill, and skirt", "[Print]")
 {
     const std::string gcode = slice({ cube(20) }, {